avformat/rdt: Check pkt_len

Fixes: CID1473553 Untrusted loop bound

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 0d0373de3b)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rdt.c

@@ -204,6 +204,8 @@ ff_rdt_parse_header(const uint8_t *buf, int len,
             return -1; /* not followed by a data packet */
 
         pkt_len = AV_RB16(buf+3);
+        if (pkt_len > len)
+            return AVERROR_INVALIDDATA;
         buf += pkt_len;
         len -= pkt_len;
         consumed += pkt_len;